1. Field of the Invention
The present invention relates to aircraft fueling systems, and more particularly, to an improved low-cost general aviation fuel control system, and will be described with particular reference thereto. However, it will be appreciated that the present invention is also amenable to other like applications.
2. Discussion of the Art
Fuel delivery systems for aircraft gas turbine engines often use a fixed, positive displacement pump to pressurize fuel from the aircraft fuel tank(s). Such a pump is generally engine driven and, as a result, provides a volumetric flow that is a function of the speed of the engine driving the pump. Thus, the positive displacement pump of an aircraft fuel system is generally sized to ensure sufficient flow capacity during all possible operating conditions.
In order to deliver accurately measured fuel flow to the aircraft engine, the pressurized fuel exiting the positive displacement pump is regulated or metered in some manner. Heretofore, metering and fuel delivery to the aircraft engine were generally accomplished by using a gearbox between the aircraft engine and the positive displacement pump and a set of valves, such as a bypass valve and a metering valve.
The use of a gearbox and multiple valves for metering and delivering fuel flow to the aircraft engine is problematic because such devices adversely impact on space constraints and increase the overall weight of the aircraft. Further, fuel systems employing these devices are often costly to manufacture and maintain.
Additionally, these types of fuel systems often require heat exchangers to keep the fuel from freezing. The necessity of heat exchangers is detrimental because these devices further increase the volume, weight, and cost of the fueling system.
The present invention provides an improved fuel system for minimizing the above-referenced and other disadvantages of the prior art.
In accordance with one aspect of the present invention, a fuel system for providing a desired fuel flow to an engine is provided. The fuel system includes a metering assembly for providing a variable portion of metered fuel flow to an associated nozzle system. The variable portion corresponds to a variable demand signal received by the metering assembly. A centrifugal pumping assembly receives fuel from an associated pumping system. The centrifugal pumping assembly pressurizes and delivers adequate fuel flow to the metering assembly. A throttling valve is in fluid communication between the metering assembly and the centrifugal pumping assembly to maintain a constant pressure rise across the metering assembly. An electronic engine control provides the variable demand signal to the metering assembly.
In accordance with another aspect of the present invention, a throttled pumping apparatus is provided for delivering pressurized fuel to an associated metering pump apparatus to maintain a consistent pressure differential across the associated metering pump apparatus. The throttled pumping apparatus preferably includes an engine shaft driven centrifugal pump and a throttling valve. The engine shaft driven centrifugal pump pressurizes and delivers a fuel output. The throttling valve reduces the fuel output before the fuel enters the associated metering pump to maintain a consistent pressure rise across the associated metering pump apparatus.
In accordance with yet another aspect of the present invention, a method of providing a desired fuel flow to an aircraft engine is provided. The method includes the steps of pressurizing adequate fuel flow, metering a variable portion of the pressurized fuel flow for delivery to the aircraft engine, and throttling the pressurized fuel flow prior to metering.
One advantage of the present invention is that it uses a simplistic design to reduce the volume and weight of an aircraft fuel system.
Another advantage of the present invention is that it uses a minimum number of parts.
Yet another advantage of the present invention is that the overall fuel system manufacturing costs are relatively low.
Still further advantages and benefits of the present invention will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description of the preferred embodiments.